In a manufacturing process of semiconductor devices, a photoresist pattern (hereinafter, simply referred to as a resist pattern) is formed on a wafer as a mask for forming a circuit pattern. The resist pattern is formed in a manner that a mask pattern is exposed onto a resist applied on the wafer, using a stepper or a scanning exposure equipment, and then an exposed portion or an unexposed portion is removed (developed). When performing fine patterning of various patterns of semiconductor devices, it is particularly important to fabricate the resist pattern with good accuracy to conform to its design dimensions as much as possible.
The resist pattern may not be properly formed as designed because of a defocus (out of focus) or the like during exposure. Specifically, the resist pattern is formed, deviating from the design dimensions. When the wafer is mounted on a mounting stage, adsorbed to maintain a surface of the wafer flat and then exposed, this defocus occurs when the surface of the wafer is not flat due to a foreign matter such as dirt and dust between the back surface of the wafer and the surface of a stage, or when the height of the resist surface is uneven for various reasons such as nonuniform application of the resist.
Conventionally, defective formation (profile error) of the resist pattern due to a defocus has been inspected utilizing diffracted light which is generated when the resist pattern is illuminated with light as diffraction grating. For example, in Japanese Patent Laid-Open Publication No. 2001-141657, presence or absence of a defocused portion is detected by capturing a color difference which is considered a diffraction angle difference of diffracted light which is generated from the defocused portion and a normal portion of the resist pattern.
As miniaturization of semiconductor devices has advanced, a pitch of the pattern formed on the wafer has become too small to generate the diffracted light using visible light. For example, in order to generate diffracted light from a fine wafer with a pitch of about 0.1 micrometers (100 nm), light in an ultraviolet region with a shorter wavelength (400 nm or shorter) than that of the visible light must be used as a light source, as described in, for example, Japanese Patent Laid-Open Publication No. 2000-338049. However, when ultraviolet light is used, the resist pattern is exposed. Further, since ultraviolet light is invisible to humans, setting of the optical system or measurement of the diffracted light requires enormous effort and time. Furthermore, an ultraviolet sensor used as a photodetector is expensive, and it is sometimes difficult to even procure an ultraviolet sensor for a large area.
Moreover, to utilize the diffracted light means that the diffraction angle is varied depending on a difference of patterns on the wafer. Specifically, it is required to carry out a macro observation in which the defective formation of the resist pattern due to defocus is observed from every angle and direction, and this has been a great disadvantage in reducing inspection time and automating the macro inspection.
An object of the present invention is to easily and highly accurately detect a profile error (deviation) of a pattern having a cross section with projections and recesses.
Another object of the present invention is to easily determine presence or absence of a defocus of a resist pattern.